1. Field of the Invention
The present invention generally relates to an image processing device which can perform a process of determining a video format more securely and rapidly. More specifically, the present invention relates to an image processing device including a video format determination section for determining a video format of a received broadcasting signal based on the number of scan lines.
2. Background Information
Current video formats for digital broadcasting include an interlacing format with 525 scan lines (480 active scan lines) (referred to as 480i), a progressive format with 525 scan lines (480 active scan lines) (referred to as 480p), an interlacing format for digital high definition broadcasting with 1125 scan lines (1080 active scan lines) (referred to as 1080i), a progressive format for digital high definition broadcasting with 1125 scan lines (1080 active scan lines) (referred to as 1080p), and the like.
In an image processing device such as a digital broadcasting receiver which receives digital broadcasting in various types of video formats, a video format of a received digital broadcasting signal has to be determined. However, conventionally, such determination has been made by measuring a number of the scan lines within a vertical interval of the received broadcasting signal.
In such a device, the measured value for the 480p video format is 1050 and the measured value for the 1080i video format is 1125, which are very close to each other. When a noise while there is no signal, or the number of the scan lines of a received broadcasting signal with a noise is measured, the noise is also measured. This may cause a problem of erroneous determination, particularly between 480p and 1080i.
A method for determining the video format is described in, for example, Japanese Laid-Open Publication No. 2004-215004.
In this determination method, when a signal standard of a decoded video signal is 525i, the count value is 78 or 79 because a horizontal frequency is 15734 Hz, and a signal which is the count value represented in a binary number is output as a frequency signal. When the signal standard of the decoded video signal is 625i, the count value is 78 or 79 because a horizontal frequency is 15624 Hz, and a signal which is the count value represented in a binary number is output as a frequency signal. When the signal standard of the decoded video signal is 525p, the count value is 157 or 158 because a horizontal frequency is 31500 Hz, and a signal which is the count value represented in a binary number is output as a frequency signal. When the signal standard of the decoded video signal is 625p, the count value is 157 or 158 because a horizontal frequency is 31250 Hz, and a signal which is the count value represented in a binary number is output as a frequency signal. A signal determination section determines a type of the decoded signal using the seventh bit and the eighth bit from the least significant bit of the above-mentioned frequency signal represented in the binary number. The counted value according to the progressive format is twice as much as that according to the interlacing format. Thus, when the counted values are converted into the binary number, 1 and 0 of the seventh bit and the eighth bit are opposite. In this way, the video format is determined.
According to the method of Japanese Laid-Open Publication No. 2004-215004, it is possible to determine whether the video format is based on the interlacing format or the progressive format. However, there is a problem that the 480p video format and the 1080i video format cannot be distinguished.
Further, for counting the number of scan lines, the number of the scan lines may be counted repeatedly for several times until the results match each other in order to prevent the erroneous determination mentioned above. Alternatively, an up/down counting method (a processing method in which the value is added by 1 when the number matches, subtracted by 1 when the number does not match, and, finally, when the value reaches +4, for example, determination of the video format is approved) may be employed. This causes a problem because it takes too much time for the determination to be made. Accordingly, it takes too much time until the image is displayed, and the user may misunderstand that there is a problem in the device.
An object of the present invention is to solve such problems by providing an image processing device which can perform a process for determining a video format securely and rapidly by determining a presence/absence of a synchronizing signal before performing the process for determining the video format. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.